When a person loses the full efficiency of one of the valves in his or her living heart, an operation is sometimes performed to implant an artificial valve. The artificial valves that are substituted for the original living tissue valves are sometimes made of animal membranes and sometimes made of metal or plastic or both. The purpose of these valves is to allow flow in only one direction, preventing back flow. These valves are usually called "check valves".
The original heart valves made of living tissue normally repair themselves, so wear is not a common problem. But, living tissue heart valves fail for other reasons. In some cases, a living tissue valve may fail to close completely when the flow pressure reverses, due to disease and/or birth defect. In any case, replacement valves are frequently required. The artificial valve that is implanted has no repair mechanism so it wears out. Eventually, it has to be replaced with a new artificial valve.
When the heart itself is replaced with a mechanical device, that is an artificial heart, the heart valves are also replaced with artificial valves. So there are two types of critical mechanisms that will wear with no living repair mechanism: the artificial heart and the mechanical check valves.
Doctors using mechanical replacement valves in animal tests of artificial hearts are finding that the mechanical valves often wear out much faster than the same mechanical valves implanted in a human heart.
The present logic in the performance of available artificial hearts is to make the heart beat at the same rate as the living heart that it replaces and to deliver the same volume as the living heart would deliver. Relatively little attention is paid to the shape of the pressure vs time graph characterizing the operation of the artificial heart, except to have the total time of pressurization approximately the same as for a living heart and except that careful attention is paid to be sure that the pressure gradient for the mechanical heart does not get so high as to injure blood cells.
Because available mechanical hearts are merely turned on and off abruptly or are possible programmed simply to avoid high pressure which would damage blood cells, they operate to transmit more shock to the mechanical valves than the living heart does, thus producing early failure of the mechanical valves.